WEBVTT 0 00:00.110 --> 00:07.010 So we're now ready to tackle our final project of the day, and that's building up a Calculator program. 1 00:07.490 --> 00:12.950 If you head over to the link for the final demo project, you can see how it works. 2 00:12.950 --> 00:18.050 So firstly, it asks us for the first number that we want to calculate with, 3 00:18.050 --> 00:20.060 so let's start with 5. 4 00:20.060 --> 00:27.440 And then it asks us to type to pick an operation + - * /. 5 00:27.440 --> 00:31.560 So let's pick a multiply by typing the asterisk sign. 6 00:31.770 --> 00:34.440 Now it asks for the next number. 7 00:34.440 --> 00:39.630 So let's say we want to multiply 5 by 3, 8 00:39.630 --> 00:41.070 so we'll type 3. 9 00:41.070 --> 00:47.160 And then once I hit Enter it will perform the operation using floating point numbers, 10 00:47.160 --> 00:49.260 and then it will give us 15.0. 11 00:49.260 --> 00:51.810 So 3 * 5 is 15.0, 12 00:51.810 --> 01:01.750 but now it asks us to type 'y' to continue calculating with the previous result, 15.0, or type 'n' to start a new 13 01:01.750 --> 01:02.710 calculation. 14 01:02.710 --> 01:04.540 So let's try the first version 15 01:04.540 --> 01:06.340 first. Let's type y, 16 01:06.340 --> 01:10.150 and now it asks us again to pick an operation. 17 01:10.150 --> 01:12.370 So notice how this is repeated, 18 01:12.370 --> 01:13.720 the same as here, 19 01:13.720 --> 01:15.100 the Step 2 here. 20 01:15.880 --> 01:19.340 So now I'm going to pick a different operation let's say add. 21 01:19.340 --> 01:21.980 And now I'm working with 15. 22 01:21.980 --> 01:26.360 So 15 plus, let's say 15 + 5, 23 01:26.360 --> 01:27.950 and let's hit Enter. 24 01:27.950 --> 01:33.680 And now it calculates our final result which is 15 + 5 = 20.0. 25 01:33.860 --> 01:43.170 So notice how in this version it took the result of the previous calculation as the first number instead 26 01:43.170 --> 01:44.580 of asking us for it. 27 01:44.580 --> 01:51.180 And then we picked an operation, and then we added the second number and it performed the calculation. 28 01:51.180 --> 01:55.380 So now we can continue working with the previous result, 29 01:55.380 --> 01:59.820 or we can type 'n' to start a new calculation. 30 01:59.820 --> 02:06.400 And again we loop back to the beginning, and we can start typing our first number, our second number, 31 02:06.400 --> 02:07.240 et cetera. 32 02:07.630 --> 02:10.090 So that's the goal for the final project. 33 02:10.090 --> 02:15.970 But before you do that, there's something I want to show that you can do with functions. 34 02:15.970 --> 02:20.410 So here I've created a function with the name add(). 35 02:20.440 --> 02:28.660 It has two inputs n1 and n2 and it outputs or returns n1 + n2. 36 02:28.690 --> 02:35.670 So you'll notice this is one of the pieces of functionality that's going to be used in our calculator, 37 02:35.670 --> 02:42.210 how to pass in two numbers to perform the addition functionality and then output the result. 38 02:42.240 --> 02:48.870 Now we've seen functions declared like this before, but what you might not have seen is the ability 39 02:48.870 --> 02:52.800 to store a function as a value of a variable. 40 02:52.800 --> 02:53.880 So what does it mean? 41 02:53.880 --> 03:00.070 Well, let's say I decided that adding numbers was my_favourite_operation. 42 03:01.060 --> 03:06.160 Now this is a variable name and you've seen us create variables like this lots of times, right? 43 03:06.160 --> 03:14.110 I could say my_favourite_operation = 3, or my_favourite_operation = "Hello", I can add strings, 44 03:14.110 --> 03:24.320 I can add various values to the right-hand side of the equal sign to add a value to a named variable. 45 03:24.350 --> 03:29.450 Now, what you might not have seen is you can also do this with functions. 46 03:29.450 --> 03:37.790 However, if we want to store a function as a value, we can't add the parentheses because as I mentioned 47 03:37.790 --> 03:42.440 before, we trigger a function with the parentheses. 48 03:42.450 --> 03:50.100 The parentheses are also obviously for adding in inputs, but if we just want to store a function to 49 03:50.100 --> 03:57.900 another name, give it another reference, then we would do it like this without the parentheses, only 50 03:57.900 --> 04:01.020 with the name of the function. 51 04:01.110 --> 04:09.040 So now what I can do is because that add() function is now stored under a new reference, my_favourite_operation 52 04:09.040 --> 04:10.150 , 53 04:10.150 --> 04:15.130 I can now trigger that function as if I was using the add() function. 54 04:15.130 --> 04:17.890 So 2 and then comma 3. 55 04:17.890 --> 04:24.130 And if I go ahead and print out the output of this result you'll see I get 5. 56 04:24.850 --> 04:26.050 So this is pretty neat, 57 04:26.050 --> 04:30.610 and it's going to be pretty important in order to create our calculator. 58 04:30.620 --> 04:34.820 So now I want you to perform the first challenge. 59 04:34.820 --> 04:38.030 And I'm going to go through the result of the first challenge, 60 04:38.030 --> 04:42.590 so we set you up correctly for tackling this project. 61 04:43.040 --> 04:54.800 So the goal is to first I want you to do this; I want you to write out the other three functions, 62 04:55.290 --> 05:03.210 it's going to be subtract(), multiply() and divide(). 63 05:03.390 --> 05:11.910 So based on what you know about functions with inputs and outputs, and also obviously these three mathematical 64 05:11.910 --> 05:18.390 operations, create the other three functions: subtract() multiply() and divide(). 65 05:18.420 --> 05:19.870 Pause the video now. 66 05:24.280 --> 05:28.810 Okay, let's go through this because this should be relatively easy to do. 67 05:28.810 --> 05:31.210 So let's first create subtract. 68 05:31.210 --> 05:34.480 And we again are going to use n1 and n2. 69 05:34.480 --> 05:37.570 And in this case we're going to return n1. 70 05:37.570 --> 05:43.460 The first number subtract the second number, so n1 - n2. 71 05:43.550 --> 05:48.200 And then we're going to create multiply again n1, n2, 72 05:48.200 --> 05:52.550 and we're going to return n1 multiply, 73 05:52.550 --> 05:59.000 so asterix, n2. And finally we're going to create divide, 74 05:59.000 --> 06:02.360 and we're going to write n1 and n2, 75 06:02.360 --> 06:08.340 and we're going to return n1 divide, which is the forward slash, n2 (n1/n2). 76 06:08.370 --> 06:09.120 So there we have it. 77 06:09.120 --> 06:12.450 We've got the other three functions created. 78 06:12.540 --> 06:16.620 Now PyCharm is screaming at me because I don't have enough spaces between the functions, 79 06:16.620 --> 06:17.910 but I'm going to write a lot more code, 80 06:17.910 --> 06:20.400 so I really want it to be compact. 81 06:20.400 --> 06:22.590 So we're just going to ignore that for now. 82 06:22.830 --> 06:36.170 Now the next challenge I have for you is to add these four functions into a dictionary as the values, 83 06:36.170 --> 06:38.510 so the dictionary will have, 84 06:38.510 --> 06:41.270 the keys of this, 85 06:42.950 --> 06:48.410 + is one key, - is another key, 86 06:48.410 --> 06:52.370 *, and finally, /. 87 06:52.370 --> 06:54.620 So these are the four keys. 88 06:54.620 --> 07:00.690 So pause the video and see if you can figure out, remembering what you learned about dictionaries in 89 07:00.690 --> 07:10.080 previous lessons, how to store each of these functions as a value in a dictionary with these four keys, 90 07:10.080 --> 07:15.630 and obviously, storing each function under the corresponding key. 91 07:15.660 --> 07:19.500 Pause the video and see if you can complete this challenge. 92 07:25.660 --> 07:28.180 Okay, let's go through the solution for this. 93 07:28.180 --> 07:32.800 Let's say I decide to create a dictionary called operations, 94 07:32.800 --> 07:37.330 and I'm going to save this as a dictionary. 95 07:37.330 --> 07:42.910 So I open up my curly braces to signify that I'm creating a dictionary. 96 07:42.910 --> 07:46.250 Now I mentioned that there are going to be four keys, right? 97 07:46.250 --> 07:52.160 So "+", "-", "*", and "/". 98 07:52.910 --> 08:00.140 Now relative to each of these keys I'm going to add the corresponding values, 99 08:00.140 --> 08:03.020 and I do that using the colon symbol. 100 08:03.020 --> 08:08.460 So the value for the key, "+" is going to be the function add. 101 08:08.460 --> 08:10.860 And then I add a comma. 102 08:10.860 --> 08:15.600 And I can do this for all four of my functions. 103 08:15.600 --> 08:21.150 Again remembering not to trigger the functions because we're storing it and we're not using it, 104 08:21.150 --> 08:23.850 so we don't want the parentheses. 105 08:25.020 --> 08:28.470 So let me finish that for the rest of them. 106 08:29.190 --> 08:32.440 And finally for divide. 107 08:33.820 --> 08:43.900 So now we've got all four of these functions for our calculator, stored inside a dictionary called operations. 108 08:44.110 --> 08:52.630 Now, just as we're able to trigger a function that's stored under a variable name, as you saw before, 109 08:52.630 --> 08:58.760 we can do the same with these functions stored inside our dictionary. 110 08:58.910 --> 09:08.330 So the final TODO that, I'm going to ask you to do before we let you go and do some independent work, 111 09:08.330 --> 09:19.130 building this project is to use the dictionary operations to perform the calculations. 112 09:19.340 --> 09:22.890 So I want you to try out multiply. 113 09:23.550 --> 09:28.380 And I want you to multiply 4 by 8, 114 09:28.380 --> 09:32.580 and to do this using the dictionary. 115 09:33.180 --> 09:39.990 So see if you can figure out how to do this using what we've covered so far in today's lesson, 116 09:39.990 --> 09:48.640 and also your knowledge of how to use dictionaries and how to access their values through their keys. 117 09:48.670 --> 09:55.210 Pause the video if you need a hint, go back to the lesson on dictionaries and see if you can figure 118 09:55.210 --> 09:58.000 it out by yourself without watching the solution. 119 09:58.690 --> 10:00.010 Pause the video now. 120 10:04.090 --> 10:12.110 Okay, so you might remember that the way that we access a value from a dictionary is we first tap into 121 10:12.110 --> 10:13.490 the name of the dictionary, 122 10:13.490 --> 10:15.980 add a set of square brackets, 123 10:15.980 --> 10:22.070 and then inside the square brackets we type the key word for word. 124 10:22.070 --> 10:30.260 So in this case, if we want to multiply our multiply() function is stored under the key which is this asterix. 125 10:30.260 --> 10:40.660 So now if I go ahead and just print this value as it is, you'll see that I get a function called multiply(). 126 10:40.870 --> 10:43.660 So that doesn't give me any results. 127 10:44.260 --> 10:55.900 But if this part is equivalent to this, then that means this is equivalent to this function. 128 10:55.900 --> 11:02.480 So now if I want to use it I just need to add the parentheses straight afterwards. 129 11:02.480 --> 11:04.640 And you can see my PyCharm hints 130 11:04.640 --> 11:06.320 already knows what I'm trying to do. 131 11:06.320 --> 11:09.320 And it's asking me for n1 and n2. 132 11:09.320 --> 11:12.680 So I want to multiply four by eight. 133 11:12.680 --> 11:15.020 So I'll just type, (4, 8), 134 11:15.020 --> 11:20.900 and then now if I run this code you'll see that it's taken the 4 and the 8, 135 11:20.900 --> 11:30.840 and it has applied the correct operation, which is multiply, and put them inside this function to 136 11:30.840 --> 11:39.600 return the value 32, which then replaces this entire function call and then gets printed out into the 137 11:39.600 --> 11:40.440 console. 138 11:41.040 --> 11:46.690 So now that we figured out how to do this, the rest is up to you. 139 11:46.720 --> 11:53.710 So take a look at the bullet points for the functionality that we need for this calculator, and look 140 11:53.710 --> 11:57.190 at the demo software to see what you need to build. 141 11:57.190 --> 12:04.180 And then pause the video and using the starting file, complete the project by yourself. 142 12:04.180 --> 12:07.810 Pause the video and complete this project. 143 12:13.820 --> 12:18.050 Okay, let's walk through the solution together so that you can check your code, 144 12:18.050 --> 12:23.660 and also, if you get stuck, it'll be a good place to try to get unstuck. 145 12:23.780 --> 12:28.010 So I'm going to work through the functionality I've listed out one by one. 146 12:28.010 --> 12:34.710 That way, we can keep track of what's going on and make sure that we achieve all of the requirements 147 12:34.710 --> 12:36.030 of this project. 148 12:36.030 --> 12:40.470 So the first one is, "Program asks the user to type the first number." 149 12:40.470 --> 12:44.130 So that is going to be an input of some sort. 150 12:44.130 --> 12:49.980 And we're going to say, "What is the first number?" 151 12:50.460 --> 12:54.270 And then we add a colon add a space so that they can type it in. 152 12:54.270 --> 12:58.510 And we'll save this to a variable called num1. 153 12:58.690 --> 13:04.570 Now next the program is going to ask the user to type a mathematical operator. 154 13:04.570 --> 13:09.430 So plus, minus, multiply, or divide. 155 13:09.430 --> 13:12.580 So now that's going to be another input. 156 13:12.580 --> 13:17.860 And this is going to be, "Pick an operation." 157 13:17.860 --> 13:20.380 And then we're going to put a space. 158 13:20.620 --> 13:27.920 And now we're going to save this inside a variable which I'll call operation_symbol. 159 13:27.950 --> 13:31.160 Now how does a user know what to type. 160 13:31.160 --> 13:35.810 How do they know that they need to type one of these symbols. 161 13:35.810 --> 13:43.520 Well if we look at the demo you can see that we actually list out all four of the operators for them, 162 13:43.520 --> 13:47.220 and that way they'll know which symbol to use. 163 13:47.220 --> 13:49.020 So how can we do that? 164 13:49.020 --> 13:57.720 Well, we could use our existing dictionary called operations to give them an idea of what to type. 165 13:57.720 --> 14:06.150 So we could, for example, use what we've learned about looping through dictionaries, "for symbol in 166 14:06.150 --> 14:07.800 operations..." 167 14:07.800 --> 14:13.000 And then for each of the symbols, we know that when we loop through dictionaries, it just gives us 168 14:13.000 --> 14:17.260 the key as the binding to the first variable. 169 14:17.260 --> 14:20.560 So then we can simply just print out the symbol. 170 14:20.560 --> 14:26.710 So let's run this file as it is and see our first input trigger, 171 14:26.710 --> 14:34.000 and then we've got each of our keys in our operations dictionary being printed out. 172 14:34.000 --> 14:37.050 And finally we get to the input 173 14:37.050 --> 14:39.810 where it asks us for the operation_symbol. 174 14:40.800 --> 14:48.930 So now we're ready to tackle this sentence, which is, "Program asks the user to type the second number." 175 14:48.930 --> 14:53.010 So let's go ahead and save this to a variable called num2. 176 14:53.010 --> 15:00.550 And it's again going to be an input which is going to say, "What is the next number?" 177 15:03.370 --> 15:11.950 And then remember that with numbers such as num1 and num2, we need to actually use it as a number in 178 15:11.950 --> 15:14.920 order for our mathematical operations to work, 179 15:14.920 --> 15:22.570 because at the moment, if we try to do, for example, num1 + num2, it's going to treat them as 180 15:22.570 --> 15:23.150 strings. 181 15:23.150 --> 15:30.710 So if I try to add 3 to 3, it's going to give me 33 instead of 6. 182 15:30.710 --> 15:38.600 And so in order for that to not happen, we need to turn these numbers into either integers or into 183 15:38.600 --> 15:39.380 floats. 184 15:39.380 --> 15:45.920 Now because we've got division and we've got subtraction and we've got multiplication, in order for our 185 15:45.920 --> 15:50.910 calculators to be a little bit more mathematical and scientific, 186 15:51.300 --> 15:56.310 let's go ahead and turn each of these numbers into floats. 187 15:56.310 --> 16:03.150 So I'm going to wrap the input for num1 and num2 both inside floats. 188 16:04.080 --> 16:12.310 And now we're ready to tackle the next part, which is where the program is going to work out the result 189 16:12.310 --> 16:19.720 based on the chosen mathematical operator, and obviously work it out based on num1 and num2. 190 16:20.080 --> 16:25.000 So that is where the part comes in that we prepped for. 191 16:25.030 --> 16:33.760 We know that we can get hold of the name of these functions by tapping into the relevant key. 192 16:33.760 --> 16:40.070 And notice that we printed out each of these keys for the user so that they would pick it for their 193 16:40.070 --> 16:41.360 operation_symbol. 194 16:41.360 --> 16:49.790 So that means we can use this operation_symbol as the key selector to pick out the correct operation. 195 16:49.790 --> 16:55.400 And that's why we went through this whole process of setting up the dictionary and setting up the methods. 196 16:55.400 --> 17:05.040 So here if we go ahead and simply just print the operations, which is our dictionary, and then 197 17:05.040 --> 17:14.280 using the square brackets passing in the operation_symbol as the key, you'll see that if I type plus 198 17:14.280 --> 17:20.670 and it doesn't really matter which number you'll see, the function that gets picked will be add(). 199 17:20.880 --> 17:30.580 But if I pick a different operation, say this one, then the function that gets selected will be multiply(). 200 17:30.610 --> 17:36.460 And all we need to do to activate it is to add the parentheses. 201 17:36.460 --> 17:44.410 And then the two numbers that we're going to pass into any of these functions will be n1 and n2. 202 17:44.410 --> 17:55.940 So let's pass num1 for n1 and num2 for n2, so that these user-generated numbers gets placed into 203 17:55.940 --> 18:03.140 whichever function they desired, and then it will output the result of that calculation. 204 18:03.800 --> 18:10.670 So let's run this code and try something like again 3 + 3. 205 18:10.670 --> 18:15.240 And now we get 6, which is a lot better than before. 206 18:15.480 --> 18:23.880 Now notice that in the demo when we do the same thing, it gives us the whole calculation, which I 207 18:23.880 --> 18:28.260 think is quite nice because then the user sees the entire equation. 208 18:28.260 --> 18:32.100 So let's replicate that in our code as well. 209 18:32.100 --> 18:42.800 So instead of just printing the result let's go ahead and create an f-string and place this calculation 210 18:42.800 --> 18:44.870 inside a set of parentheses. 211 18:44.930 --> 18:53.720 Alternatively, you can place it inside a separate variable if you think this makes it easier to understand, 212 18:53.720 --> 18:55.250 and easier to read. 213 18:55.250 --> 18:59.000 And then we can simply place the answer into the f-string. 214 18:59.120 --> 19:08.880 So our equation is going to be num1 and then space, and then the operation_symbol and then space, 215 19:08.880 --> 19:13.380 and then num2 and then finally =, 216 19:13.800 --> 19:15.720 and we get to the answer. 217 19:15.720 --> 19:19.770 So let's try this again 3 + 3, 218 19:19.770 --> 19:27.370 we get this whole equation printed out which is kind of neat I think. So the next part that we need to 219 19:27.370 --> 19:34.960 tackle is the "Program should ask the user if they want to continue working with the previous result." 220 19:34.960 --> 19:42.910 So this answer keeps the result from the first calculation num1, whatever num2. 221 19:42.940 --> 19:50.090 Now if the user wants to continue working with that number, as is usual in most calculators, 222 19:50.090 --> 19:54.440 then we want to ask them that question right about now. 223 19:54.620 --> 20:05.750 So we're going to use an input and we're going to say, "Type 'y' to continue calculating with..." 224 20:05.750 --> 20:21.480 And then we'll insert the answer from the previous step and we'll say or type 'n' to start a new calculation. 225 20:22.200 --> 20:26.670 And that way we can get hold of their request. 226 20:26.670 --> 20:34.710 Do they want to restart and type in n1 again? Or do they want to simply just type an operation_symbol 227 20:34.710 --> 20:39.700 and a num2, and use the previous answer as num1? 228 20:39.850 --> 20:46.840 Now we need to do something about this input, so let's save it into something called choice. 229 20:46.840 --> 20:54.190 And we can save the choice, which we know is going to be 'y' or 'n', and we can check the choice. 230 20:54.190 --> 21:01.820 So, "if choice == ..." and we'll check first for 'y'. 231 21:02.480 --> 21:10.880 And then in that case, that means they want to continue working with the previous answer. 232 21:10.880 --> 21:16.370 And so what we'll do is we'll set num1 to equal the answer. 233 21:16.850 --> 21:27.240 And what we need now to happen is to get them to get the symbol and the next number and then print all 234 21:27.240 --> 21:27.900 of this out. 235 21:27.900 --> 21:29.970 So something like this. 236 21:29.970 --> 21:33.690 But as you notice this is kind of repetitive. 237 21:33.690 --> 21:36.870 So what do we do when things start repeating. 238 21:36.870 --> 21:44.910 We write a loop, or we use some sort of programming way to save us from typing out or having lots of 239 21:44.910 --> 21:46.140 repeated code. 240 21:46.140 --> 21:55.240 So we could have a variable called should_accumulate so that we could decide whether or not we should 241 21:55.240 --> 22:00.400 accumulate the answer to the next round of calculations. 242 22:00.400 --> 22:10.900 And while that is true, then we will perform all of this functionality and get to the end here. 243 22:10.900 --> 22:18.890 And if again, the answer is 'y', we set num1 to equal the answer from this step. 244 22:18.890 --> 22:24.020 And then because it's a loop, it's going to go all the way back to the top. 245 22:24.020 --> 22:29.240 So that means that this num1 here can't be inside the while loop, 246 22:29.240 --> 22:36.500 and so we need to take it outside so that it doesn't overwrite this part of the code here. 247 22:37.070 --> 22:39.100 So this part will loop. 248 22:39.100 --> 22:44.080 This part will start at the very beginning when the code starts. 249 22:44.080 --> 22:51.580 So now let's run our code file and see if all the functionality up to this point works as expected. 250 22:51.580 --> 22:55.360 So I'm going to add a 3 to 3. 251 22:55.600 --> 22:58.720 And I'm basically going to keep doing this. 252 22:58.720 --> 23:02.450 So I'm going to type 'y' to keep calculating. 253 23:02.450 --> 23:05.900 And again I'm going to add 3. 254 23:05.900 --> 23:08.720 So now you can see the next stage, 255 23:08.720 --> 23:12.350 they're taking 6 which is the answer from the previous stage, 256 23:12.350 --> 23:21.080 plus the new number that I wanted to add using the operation that I selected to calculate the new answer. 257 23:21.080 --> 23:23.360 So let's try a different operation. 258 23:23.360 --> 23:29.520 Let's say we've got 9, and I want to divide it by 2. 259 23:29.520 --> 23:34.590 And now I get 4.5, which is kind of nice because I've got floats now. 260 23:34.740 --> 23:41.520 So the next thing we need to tackle is what to happen when the user types 'n' at the moment, not what 261 23:41.520 --> 23:46.560 we want because we actually haven't got anything that addresses it. 262 23:46.560 --> 23:48.810 So let's write an else statement. 263 23:49.320 --> 23:53.860 And we know that we've got this variable that controls the while loop. 264 23:53.860 --> 23:57.550 So let's go ahead and set it to False, 265 23:57.550 --> 24:03.460 if the user no longer wants to accumulate the answer and continue calculating. 266 24:03.790 --> 24:12.160 Now at this stage, it's probably also a good idea to have some new lines so that it separates what 267 24:12.160 --> 24:14.170 the user was doing before. 268 24:14.180 --> 24:22.460 So this way we get that illusion, like what we see here when we type 'n', that we restart from the beginning. 269 24:22.820 --> 24:29.990 So once that's done, though, what we need to do is to start all the way from up here. 270 24:30.020 --> 24:32.180 So how can we do that? 271 24:32.210 --> 24:41.520 Well, what if we take all of this code and wrap it inside another while loop. 272 24:41.550 --> 24:48.960 Now, while that would work, it might be a little bit confusing, and there's actually a slightly simpler 273 24:48.960 --> 24:50.400 way of doing this. 274 24:50.400 --> 24:54.240 We could create a function called calculator(). 275 24:54.240 --> 24:58.680 And this function is going to include all of this code. 276 24:58.680 --> 25:02.490 So I'm going to select all of it and then indent it in one go. 277 25:02.680 --> 25:10.210 Now what I'm going to do is I'm going to call this function inside itself, 278 25:10.210 --> 25:13.900 and this is something in programming known as recursion. 279 25:13.900 --> 25:20.110 So if you solved this project using another while loop, that is perfectly acceptable, 280 25:20.110 --> 25:22.240 and it's a perfectly good answer. 281 25:22.240 --> 25:26.500 But while we're here, another wild joke, 282 25:26.830 --> 25:29.900 I want to show you how you can also use recursion. 283 25:30.470 --> 25:36.620 So we've got this function called calculator(), which we obviously need to call outside the function 284 25:36.620 --> 25:40.850 so that it runs after the program starts. 285 25:40.850 --> 25:47.270 And then at this line it sees it, and then it goes into the definition and starts running all of these 286 25:47.270 --> 25:48.410 lines of code. 287 25:48.410 --> 25:54.810 But once it gets to here in the else statement, we're going to call calculator again. 288 25:54.810 --> 26:01.470 And what that's going to do is it's going to go to the very beginning of the calculator and try to run 289 26:01.470 --> 26:10.770 all of this code, and it will continue recursion until the user decides to choose something else. 290 26:10.770 --> 26:13.980 So let's try out this functionality. 291 26:13.980 --> 26:15.910 Our upgraded calculator. 292 26:15.910 --> 26:17.620 Let's try, 4 * 5 = 20 293 26:17.620 --> 26:22.270 . 294 26:22.270 --> 26:26.830 Let's type 'n' so that we start a new calculation. 295 26:26.830 --> 26:33.340 We've got all the space added between the previous calculation to appear as if we're starting from the 296 26:33.340 --> 26:34.030 beginning. 297 26:34.030 --> 26:37.270 And then we'll try and do a different calculation. 298 26:37.270 --> 26:40.230 What's 3 / 2? 299 26:40.500 --> 26:46.140 And now we could type 'y' to continue working with that 1.5, 300 26:46.140 --> 26:49.830 or we could type 'n' to start a new number. 301 26:49.830 --> 26:57.660 The only final thing we need to do is just to add the logo, so that when the calculator restarts up 302 26:57.660 --> 27:00.210 here, we actually see the logo. 303 27:00.210 --> 27:04.030 So let's first do our import right at the top. 304 27:04.030 --> 27:07.180 And the file is as always called art. 305 27:07.180 --> 27:14.680 And once we've got that we're going to make the print statement for the art.logo, 306 27:14.710 --> 27:18.820 the first thing that happens in our calculator program. 307 27:18.820 --> 27:20.980 So let's do a final rerun. 308 27:20.980 --> 27:25.870 And you can see we've got our calculator with our nice little logo. 309 27:25.870 --> 27:30.170 And then we got our calculation abilities. 310 27:31.820 --> 27:42.740 We can either accumulate to continue working with the previous numbers, or we can simply type 'no' to 311 27:42.740 --> 27:46.610 start calculating with a brand new number. 312 27:46.940 --> 27:48.290 So there you have it. 313 27:48.290 --> 27:52.440 That is the calculator program in its entirety. 314 27:52.440 --> 27:56.640 And if you want, you can always improve these projects. 315 27:56.640 --> 27:58.770 They are, as I say, always, 316 27:58.770 --> 27:59.970 they are learning projects. 317 27:59.970 --> 28:06.480 So they're trying to get you to use some piece of knowledge that you learnt during the day's lessons 318 28:06.480 --> 28:09.720 or previous lessons, but they're not perfect projects. 319 28:09.720 --> 28:13.920 And if you wish, you can always write more code and do more research. 320 28:13.920 --> 28:17.410 Search the internet to make it your very own version. 321 28:17.410 --> 28:23.350 But if you're satisfied with what you've learned from this lesson, and you've understood all of it 322 28:23.350 --> 28:29.650 enough to be able to build this project, or be able to understand the solution code and go back to 323 28:29.650 --> 28:35.830 build your project, then I'm happy that you've managed to get through today's content. 324 28:36.070 --> 28:40.900 So all that's left to do is rest up and I'll see you tomorrow.